Maj. Gen. Robert Mood, head of the UN observer team in Syria, stands near a UN observers car in Damascus in May.AP

BEIRUT — U.N. observers in Syria suspended their activities and patrols Saturday because of escalating violence in the country, the head of the mission said, the strongest sign yet that an international peace plan for Syria is disintegrating.

Maj. Gen. Robert Mood said rising bloodshed over the past 10 days was posing significant risks to the lives of the 300 unarmed observers in the country, and was impeding their ability to carry out their mandate.

The observers were sent to the country after international envoy Kofi Annan brokered a peace plan that included a cease-fire that was supposed to take effect on April 12. But both sides have continued to stage daily attacks and the observers themselves have been caught up in the violence on several occasions.

The U.N. observers have been the only working part of Annan’s the plan, which the international community sees as its only hope to stop the bloodshed. They were initially sent to monitor compliance with the cease-fire but ultimately became the most independent witnesses the carnage between government and rebel forces that have largely ignored the truce.

The Syrian government, intent on wresting back control of rebel-held areas, launched a fierce offensive in recent days to recover territories in several locations, shelling heavily populated districts and using attack helicopters over towns and cities.

U.N. officials have said that the opposition, in turn, is increasingly coordinating attacks against government forces and civilian infrastructure.

On Saturday, government troops kept up their relentless shelling of rebel-held districts in the central city of Homs, killing at least five. Another 12, including a man, his wife and child, were killed in overnight shelling of suburbs of the capital Damascus.

“U.N. observers will not be conducting patrols and will stay in their locations until further notice,” Mood said in a statement Saturday. He said the observers will not leave the country, and the suspension will be reviewed on a daily basis.

“Operations will resume when we see the situation fit for us to carry out our mandated activities,” he said.

The suspension signals the unraveling of Annan’s plan as the conflict that began in March 2011 with peaceful protests challenging the regime spirals closer toward civil war. Activists say some 14,000 people have been killed in the conflict.

Western powers have stuck by the plan, in part because there are no other options on the table. There is little appetite for the military intervention that helped oust Libya’s Moammar Gadhafi, and several rounds of sanctions have failed to stop the bloodshed.

The U.S. was now consulting with allies about “next steps toward a Syrian-led political transition,” National Security Council spokesman Tommy Vietor said, adding that “the sooner this transition takes place, the greater the chance of averting a lengthy and bloody sectarian civil war.”

Vietor was referring to the two U.N. resolutions that detailed Anan’s peace plan and called for political dialogue between the government and the country’s fractured opposition. He did not give further details in his statement.

Mood did not elaborate or say whether the monitors might eventually leave, but on Friday, he said states that provide the observers were concerned that the risk is approaching an unacceptable level — suggesting the violence could prompt the observers to pull out of the country at some point.

“The lack of willingness by the parties to seek a peaceful transition, and the push towards advancing military positions is increasing the losses on both sides,” Mood said. “It is also posing significant risks to our observers.”

The Syrian government said it conveyed to Mood its “understanding” of the decision taken and blamed the rebels, whom it refers to as “terrorists” for the escalation.

The Foreign Ministry said in a statement that it had “clarified to the leadership of the U.N. mission that armed terrorist groups have conducted, since the signing of the Annan plan, an increase in criminal operations that have targeted, many times, the observers, and threatened their lives.”

The opposition, for its part, has blamed the regime for the attacks near the observers.

Last week, an observers’ convoy was blocked and attacked with stones, metal rods and gunfire by an angry crowd as it was trying to head to the town of Haffa in the coastal Latakia region, where troops had been battling rebels for a week.

The observers only managed to enter once government troops had seized the area back from the rebels.

On May 15, a roadside bomb damaged observers’ cars shortly after they met with Syrian rebels in the northern town of Khan Sheikoun. A week earlier, a roadside bomb struck a Syrian military truck in the south of the country just seconds after Mood drove by in a convoy.

Still, their presence has been a crucial source of independent information, particularly as Syria bars journalists from reporting freely in the country.

Despite fears that violence could significantly worsen without the their presence on the ground, prominent activist Rami Abdul-Rahman of the Syrian Observatory for Human Rights said it was better for the U.N. teams to leave.

“We haven’t seen anything beneficial from them. If they are independent — so what?” he said. “A lot of crimes happened in Syria, and they couldn’t do anything.”

He called on the international community to more actively intervene to halt the bloodshed in Syria.

“The situation can’t get worse than this: are we afraid that it’s a civil war? Well it is a civil war. The situation is difficult. The international community’s silence on Syria is working to destroy Syria,” Abdul-Rahman said.

In the Damascus suburb of Douma, where overnight shelling killed 12 people, activist Mohammed Douma said the presence of observers had been irrelevant anyway, adding that they hadn’t visited Douma, a hotspot, in a week.

“But anyway, all they can do is record what they see, they cannot help,” he said.